Modern aircraft include electronic components to control practically every system provided on the aircraft, including the navigational, cabin pressure and environment, and power systems, as well as the individual elements which comprise those systems. Considering the relative size of the systems needed to operate modern aircraft, the size of the electronic systems, including not only the individual electronic components, but the electrical buses interconnecting the individual electronic components, need to be sized accordingly. Such large electronic components necessarily generate large amounts of heat which need to be dissipated quickly in order to maintain effective operation of the aircraft systems.
In the prior art, attempts to dissipate the heat have included heat exchangers employing conventional heat sinks having a plurality of metal fins or other surface area increasing structures for thermal conduction and dissipation. One problem with such devices, however, is that given the huge demand for heat dissipation of modern aircraft systems, the metal heat sinks must be accordingly sized. This results in a cooling system having excessive weight and space requirements, and thus a less efficient, if not impractical, aircraft.
The prior art therefore has evolved to include thermosyphons to cool the electronic components. As disclosed in U.S. Pat. No. 5,240,069, typical thermosyphons include a liquid coolant which cycles between an evaporator section and a condenser section. The evaporator section is provided in thermal communication with the heat source, in the present application being the aircraft electronics, while the condenser section is provided in thermal communication with a heat sink, such as fins or passing liquid or gaseous coolant, to dissipate the heat. A rotating heat pipe connects the evaporator section to the condenser section such that when the liquid coolant within the evaporator section is heated by the heat source and vaporizes, the vaporized liquid rises to the condenser section wherein the vaporized liquid cools and condenses on the side walls of the heat pipe. The rotation and slant of the heat pipe creates centrifugal force which causes the condensed liquid to flow along the pipe walls back to the evaporator section to continue the cycle.
While such a thermosyphon can certainly dissipate more heat than a system employing extruded metal heat sinks, the heat dissipation burden of modern aircraft electronics, as well as the critical nature of maintaining proper operation of the electronics, dictates the use of multiple thermosyphons for the individual electronic components. For example, if a three phase electric motor drive is to be cooled, a separate thermosyphon is often used to cool each individual phase. This adds additional weight and requires additional space, which the aircraft often cannot provide.
Furthermore, if the aircraft is intended for military use, the thermosyphons will necessarily be subjected to battle damage or loss. It is therefore necessary to oversize the individual thermosyphons to adequately handle the dissipation demand of the other phases in the event that one thermosyphon is damaged or lost. Similarly, if one of the phases should fail or be damaged, the work load of the remaining phases will be increased accordingly. Since prior art systems are designed to have each thermosyphon dedicated to a single phase, the thermosyphons dedicated to the remaining operational phases need to be oversized to handle the additional heat dissipation burden created by the additionally burdened phases. No form of load sharing between the operational thermosyphons currently exists to alleviate this problem.
As disclosed in U.S. Pat. No. 4,951,530, systems have been designed to enhance the heat dissipation capabilities of conventional thermosyphons. Heat fins can be added to the condenser and evaporator sections to thereby increase the total surface area of the heat exchanger. Additionally, the entire thermosyphon can be surrounded by a coolant such as a fluorocarbon to thereby lower the ambient temperature in which the thermosyphon operates. While such systems can increase the heat dissipation capacity of the system, each requires additional space and adds additional weight.